This invention relates to the art of cleaning hot forming dies and, more particularly, to new and improved processes for the rapid and contaminate-free cleaning of lubricants and other foreign matter from hot working surfaces of superplastic and quick plastic forming dies to enhance the production of formed sheet metal parts with high quality show surfaces.
Prior to the present invention, various processes and types of equipment have been developed to form sheets of alloys of aluminum and other suitable metallic materials into panels or other parts for vehicles or other constructions. Among such process and equipment are super and quick plastic forming processes and equipment in which a ductile metal sheet of suitable metallic material is heated and stretched onto the forming surfaces of a hot die to improve production of high quality parts. Examples of such processes and equipment are found in U.S. Pat. No. 5,974,847 issued Nov. 2, 1999 to Saunders et al. for Superplastic Forming Process, and U.S. Pat. No. 5,819,572 issued Oct. 13, 1998 to P. E Krajewski for Lubricating System For Hot Forming, both assigned to the assignee of this invention and both hereby incorporated by reference.
While such hot plastic forming processes and equipment provide improved parts, production efficiency has at times been diminished because of rejection of some parts for indentations and other irregularities occurring in the show surfaces thereof. Such surface imperfections are primarily caused by the accumulation of foreign matter and particularly dry lubricants used on the blank sheets of material on the hot die during the hot superplastic forming processes. Such matter accumulating on the precision forming surface of the hot die deforms the hot outer surfaces of the part being formed under the loads of the superplastic or quick plastic processes.
In contrast to the prior art, the present invention provides new and improved methods and mechanisms that meets higher standards for cleaning hot superplastic and quick plastic forming dies while in the press and operating at elevated temperatures. More particularly, the invention is directed to the effective removal of accumulated foreign matter and particularly dry lubricants so that such foreign matter does not effect the formation of flaws such as lubrication marks in the outer surfaces or tears in the bends of the parts formed by the die.
This invention provides new and improved CO2 hot die cleaning methods with the controlled discharge of dry ice which at least partially sublimes and impinges on the surface of a heated forming die to contact and displace foreign matter from the surface of the forming die so that the forming die can be quickly operated to again produce parts with Class A part surface quality. This invention eliminates lubricant and oxide build-up on the die surfaces and provides a significant improvement in the efficient and quantity production of Class A quality surfaces on metallic parts and panels formed by the dies. Importantly, there is no liquid residue or other consequential pollution produced by this process. The cleaning procedure for dry cleaning forming dies reduces cleaning frequency with minimized CO2 consumption to provide improved operating efficiency.
This invention further provides a new and improved hot die cleaning unit comprising a special end effector for discharging streams of CO2 gas and solid mixed into streams of pressurized air onto the hot surface of the die operatively mounted in a press when the press is open. The unit features the quick attachment and release of the end effector to a programmed robot operable to move the discharge end of the end effector across the die in a controlled pattern and at a predetermined distance from the forming surface with optimized discharge of the carbon dioxide and air cleaning mixture to decrease the cycle time required to complete effective cleaning of hot die surfaces during the production cycling of such dies.